The present invention relates to high performance racing engines and more particularly, to an improved valve lifter for such racing engines.
Conventional camshaft internal combustion engines typically utilize valve lifters, push rods and valve springs along with rocker arms to open and close the valves of the engine to allow air and fuel to enter and exhaust to exit the cylinders of the engine during combustion. The valve lifter with a pushrod includes a cam roller, which rides on the lobes of a camshaft, which is rotated by the crankshaft. In typical roller type valve lifters, the force generated as the cam lobe drives the roller and associate valve lifter body to its valve opening position, is transferred to the valve lifter body through a pin that mounts the roller to the valve lifter body. The entire force imparted on the lifter body during reciprocation of the valve lifter is borne by the bearing and associated pin. As the lifter reciprocates up and down, the push rod seated in the lifter also reciprocates and transfers this up and down motion via a rocker arm to either an intake or exhaust valve.
During the up stroke of the piston in the cylinder, the intake valve opens to allow fuel and air to enter the combustion chamber. Somewhere near the very top of the up stroke, both the intake and the exhaust valves close and the spark plug creates a spark to ignite the air-fuel mixture which is under compression by the piston. This results in a high temperature explosion which forces the piston downward, called the xe2x80x9cpower stroke,xe2x80x9d thereby translating this movement via a connection rod to rotate the crankshaft which, in turn, translates this angular motion to the wheels of the vehicle via a set of gears. Near the bottom of the compression stroke, the exhaust valve opens to expel the burnt fuel mixture out of the cylinder. After the piston changes directions and begins the up stroke, the exhaust valve continues to remain open thereby forcing any remaining the spent gases out of the cylinder. However, during this same time, the intake valve begins to open to recharge the cylinder with fuel. It is not until the piston has started to travel upward that the exhaust valve closes. Thus, at various times during the compression cycle, both the intake and exhaust valves will be open and closed at the same time. The timing of the opening and closing of the valves is controlled by the physical design of the oval shaped lobes on the camshaft. As the valve lifter is pushed upward by the lobe of the camshaft, the valve lifter pushes the pushrod up which drives the rocker arm downward, causing the valve to open. Likewise, as the lifter and pushrod travel downward, the rocker arm raises and the valve closes due to the biasing action of the valve spring.
In the operation of high-speed engines, measured as revolutions per minute (RPM), the valve train components are under extreme stress and high temperatures. This causes high frictional forces to be imparted on the cam roller via the cam lobe of the camshaft. Overall cam roller wear is a function of engine speed. High performance engines such as those used in drag racing applications produce extremely high engine speeds (6,000 to 13,000 RPM) over a short duration of time (i.e. less than 5 to 12 seconds). At these high engine speeds, it becomes difficult for the cam roller, pin and the associated bearings to withstand the stress of the engine and, therefore, subsequently fail. Cam rollers and associated pin often fail prematurely in racing situations due to this excessive force causing the valve lifter to be replaced between successive races. Therefore, there is a need for a valve lifter design that can withstand the stress of high performance engines used under racing conditions.
In addition, inadequate oiling of the bearings will also result in excessive wear and may lead to failure of the bearings, and consequently failure of the valve lifter. A known approach to oiling the bearings is to provide oil feed bevels in the body of the valve lifter that houses the roller. This oil feed bevel allows oil to flow into the distal end of the valve lifter towards the shaft and bearings. While this method attempts to provide oil to the cam roller bearing, oil may not be present in this area or may be directed away from the shaft and bearing due to the rotation of the cam. Therefore, there is a need for a valve lifter design which improves the oiling of the cam roller bearings to prevent premature failure of the cam roller, especially in racing engines where high RPMs are obtained.
The present invention relates to a valve lifter for an internal combustion engine, particularly for use in high performance in racing applications. The valve lifter includes a body adapted to be reciprocally slidable within a valve lifter bore forming part of the engine. The valve lifter also includes a cam roller and an auxiliary roller rotatably mounted in the lifter body. The cam roller engages the cam lobe of the cam-shaft for driving valve lifter body to open the associated valve. The auxiliary roller is mounted in the lifter body and engages the cam roller is such manner that the force of the cam lobe on the cam roller is transferred to both the cam roller and auxiliary roller such that neither roller bares the total force of the cam lobe individually.
In a preferred embodiment, the cam roller and auxiliary roller are secured in the lifter body by pins. These pins allow the force from the cam lobe to be transferred from the rollers to the valve lifter body to open the associated valve.
In another embodiment of the present invention, the valve lifter body includes a recess to house the cam roller. This recess includes grooves in the walls of the recess to allow oil to be directed into the recess. Oil is needed in this area of the lifter body to lubricate the bearings of the cam roller. In addition, an auxiliary roller can be included in the upper portion of the recess. The auxiliary roller is in rolling engagement with the cam roller. The grooves in the recess wall allow oil to be introduced to the upper region of the recess, which, in turn, allows the bearings of the auxiliary roller to be lubricated. This lubrication feature increases the life of the valve lifter.
The present invention is also directed to a method of milling the recess of a valve lifter such that grooves remain on the walls of the recess for lubricating the bearings of the rollers. The method involves drilling holes in the body of the lifter where the recess is to be formed. A milling cutter is used to create the recess. The milling cutter does not mill to the outer edges of the holes, thus, upon completion grooves will remain at the four corners of the recess.